In general, a pressure relief valve may be designed to open at a specific pressure to prevent pressures in a system from exceeding certain limits. Pressure relief valves are widely used in a variety of applications. Pressure relief valves may be used for the purpose of providing safe operation in high pressure environments, for example, in hydraulic systems. Pressure relief valves may also be used to establish a known pressure for the purpose of providing control over a process, flow or motion. One example of an application for a pressure relief valve is a shock absorber application such as the semi-active shock absorber control system disclosed in U.S. Pat. No. 6,732,033, which is fully incorporated herein by reference.
Electrically controlled pressure relief valves may include an actuator that is electrically controlled, for example, in response to a command. Existing electrically controlled pressure relief valves may control the valve actuator electrically based upon a desired output pressure of the valve. While such electrically controlled pressure relief valves provide performance advantages, such as safety and known set pressure nearly independent of flow, there may also be disadvantages. Existing electrically controlled pressure relief valves may be unstable or may have a very long response time. The instability can be attributed to the interaction of the output pressure variation of the valve with other hydraulic system components such as the hydraulic compliance in the system or the inertia of the hydraulic fluid running in the hoses. To mitigate the instability, those of ordinary skill in the art may change the command to the valve slowly, reduce the system compliance or inertia, and/or slow down the step response of the valve to the command by adding a large amount of damping.
Another approach to providing control in a hydraulic system is to utilize a position-based valve that is controlled externally by electronics but is not hydraulically assisted with a pressure term. Such a valve may include precision machined components to shape the valve orifice geometry as a function of position. In practice, these valves can achieve a high level of control from a precision stand-point; however, the bandwidth is still very low because large amounts of damping may be required to avoid instability. These valves are also expensive, and since they are multi-stage, may require a high pressure source to function at any level of performance.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the subject matter be viewed broadly.